Apparatus for forming a thin film

ABSTRACT

An apparatus for forming a thin film having a vacuum container evacuated to high vacuum and receiving a gas for vapor deposition, a generation device for generating a material vapor, a counter electrode holding a substrate to be vapor-deposited, a first grid disposed between the generation device and the electrode for accelerating the vapor, and a filament for emitting thermions to ionize the vapor. The first grid and counter electrode surfaces may be curved and parallel to each other, and a second grid for accelerating the vapor, having a potential which is negative with respect to the potential of the first grid, may be placed between the first grid and the electrode, in the vicinity of the electrode, and a device may be provided for moving the first grid with respect to the electrode on a predetermined track.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for forming a thin filmwhich is suitable for forming a metal thin film or a semiconductor thinfilm which constitutes an IC, LSI or the like.

Various means for forming a thin film on a substrate have conventionallybeen proposed and various methods have been adopted therefor CVD andPVD, for example, are typical of those methods.

CVD is advantageous in the strong reactivity, while PVD is advantageousin that it enables film formation in a high vacuum, thereby forming adense and strong film. On the other hand, CVD disadvantageously requiresthe temperature of the substrate to be kept high, and the formation of areactive thin film is difficult by PVD except for a part of the ionplating methods, as is well known to those skilled in the art.

An ion plating method is a method of ionizing and evaporating in vacuumthe substance evaporated in an active gas or an inert gas by producing ahigh-frequency electromagnetic field between a source of evaporation andsubstances being evaporated. The ion plating method includes DC ionplating method in which a DC voltage is applied between the source ofevaporation and the substances being evaporated. These ion platingmethods are disclosed in, for example, Japanese Patent Publication No.52-29971 (1977) and 52-29091 (1977).

Japanese Patent Application Laid-Open (KOKAI) No. 59-89763 (1984) filedby Applicant discloses an apparatus for depositing a thin film. Thisapparatus is provided with a counter electrode for holding a substratefor deposition, and a grid disposed between the counter electrode and asource of evaporation which opposes the counter electrode in such amanner that the grid is impressed with a positive potential relative tothe counter electrode. A filament for thermionic emission is disposedbetween the grid and the source of evaporation. This structure enablesthe substances evaporated from the source of evaporation to be ionizedby the thermions emitted from the filament. The ionized substances whichpass through the grid are accelerated by the effect of an electric fielddirected from the grid to the counter electrode and impinge on thesubstrate, thereby forming a thin film having a good adhesion on thesubstrate.

There are many other methods of and apparatuses for forming a thin film.However, the conventional methods of forming a thin film have someproblems.

A first problem is that the adhesion between the thin film formed andthe substrate is weak.

A second problem is that it is difficult to form a thin film on asubstrate having a low heat resistance.

A third problem is that if a material having a low electric conductivityand having a large area such as a plastic film and a disk is used as asubstrate for deposition, there is difference in physical properties ofthe thin film formed such as the thickness and the electrical resistancebetween the central portion and the peripheral portion of the substrate.

In a conventional apparatus for forming a thin film having the thirdproblem, the reason why the thin film formed produces difference inphysical properties such as the thickness and the resistance between thecentral portion and the peripheral portion of the substrate fordeposition is as follows:

The surface of the counter electrode has an equal potential at allpoints and the electric field is orthogonal to the surface However, whenthe substrate for deposition which is thick to a certain extent andinferior in the electric conductivity is held by the counter electrode,the electric field on the surface of the substrate is not alwaysorthogonal to the surface of the substrate, so that the states of theelectric field are not the same between the central portion and theperipheral portion of the substrate.

The nature of the plasma generated at the central portion of thesubstrate is therefore different from that generated at the peripheralportion of the substrate, which fact leads to the difference in thephysical properties of the thin film formed such as the thickness andthe resistance between the central portion and the peripheral portion ofthe substrate for deposition. Especially, in the case of the methoddisclosed in Japanese Patent Application Laid-Open (KOKAI) No. 59-89763(1984), when the pressure of the gas introduced at the time of filmformation is low or when the distance between the grid and the substrateis short, the evaporated particles reach the substrate while thedispersion of the particles due to the ambient gas or ions isinsufficient, so that the film thickness is insufficient at the portionat which the material constituting the grid shields the evaporatedparticles.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the present invention to provide anapparatus for forming a thin film which is capable of forming a thinfilm having a strong adhesion on a substrate and which is capable ofusing a material having a low heat resistance such as a plastic sheetfor the substrate.

It is a second object of the present invention to provide an apparatusfor forming a thin film which is capable of forming a thin film having astrong adhesion on a substrate and excellent uniformity and which iscapable of using a material having a low heat resistance such as aplastic sheet for the substrate.

According to the present invention, the first object can be achieved bythe first apparatus, that is,

an apparatus for forming a thin film comprising;

a vacuum container evacuated to high vacuum and receiving a gas forvapor deposition therein,

generation means for generating a vapor of a material for vapordeposition and introducing said vapor into said container,

a counter electrode disposed within said container and holding asubstrate to be vapor-deposited on a holding surface thereof, saidholding surface opposing said generation means with a substantiallyequal distance from said generation means at all points thereof, anelectrical potential of said electrode being to be set equal or negativerelatively to an electrical potential of said generation means, saidholding surface being adapted to have a parallel curved surface,

a grid disposed between said generation means and said electrode forallowing said vapor to pass therethrough and accelerating said vapor, asurface of said grid being adapted to have an equal distance from saidholding surface, an electrical potential of said grid being set positiverelatively to said potential of said generation means, said grid beingadapted to have a parallel curved surface, and

a filament disposed between said generation means and said grid foremitting thermions to ionize said vapor.

According to the first apparatus, electric fields directed in theopposite directions, namely, an electric field directed from the grid tothe substrate and an electric field directed from the grid to thegeneration means are formed in the vacuum container. Since the surfaceof the grid with a parallel curved surface has a configuration having anequal distance from the holding surface with a parallel curved surfaceat all points, the electric field directed from the grid to thesubstrate is generated substantially perpendicularly to the holdingsurface. Preferably the parallel curved surface is a concentric spheresurface.

A part of the vapor from the generation means is ionized to cations bythe thermions emitted from the filament. The vapor partially ionized inthis way passes through the grid and the ionization of the vapor tocations is further accelerated by ionized gas. The effect of theelectric field accelerates the speed of the cations to be impinged ontothe substrate.

Since the ionization of the vapor generated from the generation means iseffected in a very high state by the thermions from the filament and theelectric fields in the vicinity of the grids, a very stable plasma stateis realized. At this time, since the electric field directed from thegrid to the substrate is generated substantially perpendicularly to theholding surface, and the vapor has charges, the course of the cations ischanged by the electric field in such a manner as to be along theelectric field.

Consequently according to the first apparatus, the ionized vaporproceeds in the direction of the electric field and impinges onto thesubstrate substantially perpendicularly thereto at an accelerated speed,so that a thin film which is excellent in the adhesion, the surfacesmoothness and crystallizability is formed on the substrate.

Further, according to the first apparatus since the thermions from thefilament are emitted in the state in which the thermions have a kineticenergy which corresponds to the temperature of the filament, they arenot immediately absorbed by the grid having a positive potential butfirst pass through the grid. Thereafter, they are brought back to thegrid by the Coulomb attraction, and pass through the grid again. In thisway, the vibrating motion is repeated around the grid, until thethermions are absorbed by the grid, so that they do not reach thesubstrate. The substrate is therefore not shocked by the thermions and,hence, not heated thereby. Thus, it is possible to prevent the rise inthe temperature of the substrate, while the vapor has a very high energydue to the high ionization. Consequently according to the firstapparatus, it is possible to form a thin film at a low temperaturewithout adding a heat energy to the substrate, thereby enabling even aplastic sheet or the like which is inferior in the heat resistance to beused as the substrate.

According to the present invention, the second object can be achieved bythe second apparatus, that is,

an apparatus for forming a thin film comprising;

a vacuum container evacuated to high vacuum and receiving a gas forvapor deposition therein,

generation means for generating a vapor of a material for vapordeposition and introducing said vapor into said container,

a counter electrode disposed within said container and holding asubstrate to be vapor-deposited such that said substrate opposes saidgeneration means,

a first grid disposed between said generation means and said electrodefor allowing said vapor to pass therethrough and accelerating saidvapor, an electrical potential of said first grid set positiverelatively to an electrical potential of said electrode,

a second grid disposed between said first grid and said electrode withina vicinity of said electrode for allowing said vapor to passtherethrough and accelerating said vapor, an electrical potential ofsaid second grid set negative relatively to said potential of said firstgrid, and

a filament disposed between said first grid and said generation meansfor emitting thermions to ionize said vapor.

According to the second apparatus, the ionization of the vapor fromgeneration means is effected in a very high state by the thermions fromthe filament, so that a thin film which is excellent in the adhesion,the surface smoothness and crystallizability is formed on the substrate.In this case, since the vapor has a very high energy due to the highionization, it is possible to form a thin film at a low temperaturewithout adding a heat energy, thereby enabling even a plastic sheet orthe like which is inferior in the heat resistance to be used as thesubstrate as in the case of the first apparatus.

In addition according to the second apparatus, there is provided asecond grid disposed in close proximity to the counter electrode. Thatis, the second grid is in close proximity to the surface of thesubstrate which is held by the counter electrode.

By the effect of the second grid, very uniform plasma is realized in thevicinity of the substrate. In addition, the vapor is uniformly shieldedby the second grid when it is impinged onto the substrate. It istherefore possible to form a uniform thin film even if the substrate isthick to a certain extent, insufficient in the electric conductivity andhas a large area.

Consequently according to the second apparatus, it is possible to form auniform thin film even on a substrate for deposition having a largearea, wherein the uniform thin film has a strong adhesion on thesubstrate and is capable of using a material having a low heatresistance such as a plastic sheet for the substrate.

According to the present invention, the second object can be alsoachieved by the third apparatus, that is,

an apparatus for forming a thin film comprising;

a vacuum container evacuated to high vacuum and receiving a gas forvapor deposition therein,

generation means for generating a vapor of a material for vapordeposition and introducing said vapor into said container,

a counter electrode disposed within said container and holding asubstrate to be vapor-deposited such that said substrate opposes saidgeneration means,

a grid disposed between said generation means and said electrode forallowing said vapor to pass therethrough and accelerating said vapor, anelectrical potential of said grid set positive relatively to anelectrical potential of said electrode,

a filament disposed between said grid and said generation means foremitting thermions to ionize said vapor, and

moving means for moving said grid with respect to said electrode on apredetermined track.

According to the third apparatus, the ionization of the vapor fromgeneration means is effected in a very high state by the thermions fromthe filament, so that a thin film which is excellent in the adhesion,the surface smoothness and crystallizability is formed on the substrate.In this case, since the vapor has a very high energy due to the highionization, it is possible to form a thin film at a low temperaturewithout adding a heat energy, thereby enabling even a plastic sheet orthe like which is inferior in the heat resistance to be used as thesubstrate as in the case of the first or the second apparatus. Inaddition according to the third apparatus, since moving means whichmoves the grid on a predetermined track relative to the counterelectrode is provided, the geometrical pattern drawn by the gridproduces the effect of shading the substances uniformly at each portionof the substrate during the formation of a thin film, thereby decreasingthe unevenness in the film thickness.

Consequently according to the third apparatus, it is possible to form auniform thin film even on a substrate for deposition having a largearea, wherein the uniform thin film has a strong adhesion on thesubstrate and is capable of using a material having a low heatresistance such as a plastic sheet for the substrate.

As for the gas for vapor deposition according to the present invention,an active gas, an inert gas or a mixture of the active gas and the inertgas may be used in any one of the apparatuses according to the presentinvention.

As for the generation means according to the present invention, thegeneration means may comprise a source of evaporation of either aresistance heating type or an electron beam type for evaporating asubstance, alternatively the generation means may comprise anevaporation injector for injecting an evaporated substance in any one ofthe apparatuses according to the present invention.

As for the grid and the holding surface according to the firstapparatus, the grid and the holding surface may be so formed as to havea concentric sphere or a parallel curved surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of the presentinvention;

FIG. 2 is a schematic view of a second embodiment of the presentinvention;

FIG. 3 shows an example of a movable grid in the second embodiment ofthe present invention; and

FIG. 4 is a schematic view of a third embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be explainedhereinunder with reference to FIG. 1. In FIG. 1, there is a vacuumcontainer 1. The vacuum container 1 is composed of a base plate 2 and abell jar 3 integrally provided on the base plate 2 through a packing 4.The base plate 2 has a hole 2a at the central portion thereof and isconnected to an evacuation system (not shown) via the hole 2a in anairtight relationship.

In the container 1, a counter electrode 5, a grid 6, a filament 7 and ageneration portion 8 for generating a vapor of a material for vapordeposition are disposed with an appropriate space therebetween in thatorder from the top to the bottom. These members 5, 6 and 7 are supportedby the electrodes 9, 10 and 11, respectively, which also serve as thesupporters. These electrodes 9 to 11 extend to the outside of thecontainer 1 through the base plate 2 while being kept electricallyinsulated from the base plate 2. These electrodes 9 to 11 electricallyconnect and feed the members inside and outside of the container 1 andcan constitute the electrically conducting means together with otherwiring means. Airtightness is secured at the portions through which theelectrodes 9 to 11 extend to the outside of the container 1.

The generation portion 8 may be a source of evaporation which is used inordinary vacuum evaporation, namely, a source of evaporation of aresistance heating type or a source of evaporation of an electron beamtype. Alternatively, an evaporation injector made of a stainless steelpipe with one end formed into a nozzle may be used for evaporating avapor of a material for vapor deposition. In the case of using such anozzle system, the other end of the steel pipe is connected to a bomb(not shown) which accommodates a material of a thin film, or a pluralityof bombs (not shown) through a gas mixer depending upon the compositionof a thin film to be formed. The generation portion 8 is connected to aterminal having a negative potential relative to the potential of thegrid 6. The generation portion 8 introduces the material of the thinfilm in the form of vapor (gas) or spray.

To the vacuum container 1, a bomb 12 accommodating an active gas such asO₂ is connected through a valve 13, and a bomb 14 accommodating an inertgas such as Ar is connected through a valve 15.

The counter electrode 5 supported by the electrode 9 has an undersurfacewhich serves as a holding surface 5a. The holding surface 5a is sodesigned as to have a substantially equal distance from the generationportion 8 at all points thereof. For example, the holding surface 5a isa sphere or a parallel curved surface. On the holding surface 5a havingsuch a configuration, a substrate 16 on which a thin film is formed isheld by an appropriate means in the state of opposing the generationportion 8.

The filament 7 supported by the pair of electrodes 11 generatesthermions which are used for the ionization of a part of the materialvapor, and is made of tungsten or the like. The filament 7 is composedof, for example, a plurality of filaments arranged in parallel orreticulately, and is so adapted as to cover the spread of the vapordischarged from the generation portion 8.

The grid 6 supported by the electrode 10 has a structure having spaceswhich allow the vapor to pass therethrough. For example, the grid 6 hasa reticulate configuration. The surface of the grid 6 is so formed as tohave an equal distance from the holding surface 5a at all points. Forexample, the grid 6 is so formed as to have a concentric sphere or aparallel curved surface. In this embodiment, the grid 6 has a structureof reticulate and a surface shape of a concentric sphere correspondingto the surface holding surface 5a.

A power source means 17 for establishing a predetermined potentialrelationship between the counter electrode 5, the grid 6, the filament7, and the generation portion 8 is provided outside the container 1 andconnected to each member through the electrodes 9 to 11. DC powersources 18 and 19 are provided, and the positive electrode of the DCpower source 18 is connected to the grid 6 via the electrode 10 and itsnegative electrode is grounded, while the positive electrode of the DCpower source 19 is grounded and the negative electrode thereof isconnected to the counter electrode 5 via the electrode 9. The grid 6 hasa positive potential relative to the potentials of the counter electrode5 and the generation portion 8. Therefore, electric fields directed inthe opposite directions, namely, an electric field directed from thegrid 6 to the counter electrode 5 and an electric field directed fromthe grid 6 to the generation portion 8 are generated in a container 1.The filament 7 is connected to both ends of an AC power source 20 viathe pair of electrodes 11. In place of the AC power source 20, a DCpower source may be used. These power sources 18, 19 and 20 constitutethe power source means 17, but the grounding shown in FIG. 1 is notnecessarily required.

Actually, the power source means 17 includes various switches foreffecting electrical connections and by operating these switches thefilm forming process is executed, but these switches are omitted here.

A method of forming a thin film using this embodiment will now beexplained.

The substrate 16 is first set and supported by the counter electrode 5,as shown in FIG. 1. The container 1 has been evacuated in advance to10⁻⁵ to 10⁻⁶ Torr and an active gas, an inert gas or a mixture of anactive gas and an inert gas is introduced thereinto, depending on cases,at a pressure of 10⁻² to 10⁻⁵ Torr. For clarity of explanation, it isassumed here that the introduced gas is an inert gas such as argon.

If the power source means 17 is operated in this state, a positivepotential is applied to the grid 6, a negative potential is applied tothe counter electrode 5, and a current flows on the filament 7. Thefilament 7 is heated by the self resistance heat and emits thermions Theargon molecules within the container 1 collide with the thermionsemitted from the filament 7 and the electrons in the outer shell of theargon molecules are fillipped out, thereby the argon molecules areionized to cations.

In this state, the vapor is introduced from the generation portion 8 tothe container 1 and a part of the activated vapor is ionized to cationsby the ionized argon or the thermions. The vapor a part of which hasbeen ionized in this way passes through the grid 6. At this time, theionization of the vapor is further accelerated by the thermions whichkeep on the vertical vibrating movement in the vicinity of the grid 6and the collision with the ionized argon gas introduced. Since thethermions from the filament 7 are emitted with a kinetic energy whichcorresponds to the temperature of the filament 7, they are notimmediately absorbed by the grid 6 having a positive potential but firstpass through the grid 6. Thereafter, they are brought back to the grid 6by the Coulomb attraction, and pass through the grid 6 again. In thisway, the vibrating motion of the thermions is repeated around the grid6.

The part of the vapor which has passed through the grid 6 and has notyet been ionized is ionized to cations by the collision with the ionizedargon gas introduced between the grid 6 and the substrate 16, therebyenhancing the ionization ratio.

The vapor ionized to cations in this way is accelerated toward thesubstrate 16 by the effect of the electric field directed from the grid6 to the counter electrode 5, and impinges and adheres onto thesubstrate 16 with a high energy. Thus, a thin film having good adhesionis formed on the substrate 16. In this embodiment, since the surface ofthe grid 6 is so formed as to have an equal distance from the substrateholding surface 5a at all points, for example, the grid 6 is so formedas to have a concentric sphere, the electric field directed toward thecounter electrode 5 is generated substantially perpendicularly to thesubstrate holding surface 5a. The vapor which has been ionized tocations also hit the substrate 16 substantially perpendicularly to thesubstrate 16 in correspondence with the direction of the electric field,thereby forming a good thin film.

On the other hand, most of the thermions emitted from the filament 7 arefinally absorbed by the grid 6 and only a part of them passtherethrough. The few thermions which have passed through the grid 6 aredecelerated between the grid 6 and the substrate 16 by the effect of theelectric field, so that almost no thermion reaches the substrate 16.Even if some of them reach the substrate 16, they do not provide thesubstrate 16 with electron impact, thereby enabling the prevention ofthe rise in the temperature of the substrate 16, thereby enabling amaterial having a low heat resistance such as a plastic material to beused for the substrate 16.

As described above, according to the first embodiment, since theionization ratio of the vapor is very high, it is easy to form a thinfilm having desired physical properties even in a case that an activegas is introduced into the container 1 singly or together with an inertgas and that the vapor and the active gas are combined with each otherso as to form a thin film of the reaction compound. For example, ifargon and oxygen are selected as the inert gas and the active gas,respectively, while the pressure in the container 1 is adjusted to 10⁻⁴Torr, and a metal such as zinc, aluminum, tin, indium and otheroxidizable metals is evaporated from the generation portion 8, a thinfilm of an oxide of such a metal, for example, zinc oxide, aluminumoxide, tin oxide and indium oxide is formed on the substrate 16.Similarly, if a metal such as titanium, chromium and iron is evaporatedand an active gas such as nitrogen and ammonia are introduced, a thinfilm of a metal nitride, namely, titanium nitride, chromium nitride,iron nitride or the like is formed on the substrate 16. Furthermore, ifargon is introduced as the inert gas and gaseous SiH₄ is used as thevapor or Si or SiO is selected as the substance being evaporated, a thinfilm of SiO₂ is formed on the substrate 16. If H₂ S and Cd are selectedas the gas and the substance being evaporated, respectively, a thin filmof CdS is obtained. If ammonia is used as an active gas together withargon, and Ti or Ta is selected as the substance being evaporated, athin film of TiN or TaN can be obtained.

The vapor is selected in accordance with the composition of a thin filmto be formed. For example, when a silicon thin film is formed, SiH₄,SiCl₄ +2H₂ or the like is used. When a thin film of SiO₂ is formed, SiH₄+O₂ is introduced as the vapor. For forming a carbon thin film, almostall organic matters containing carbon are usable. For example, alcohols,benzenes, an aqueous solution of alcohol, and organic gases such asmethane gas are usable At the time of the formation of a metal thinfilm, metal halides (e.g., CuCl₄ for the formation of a Cu thin film andAeCe₃ for the formation of an Ae thin film) or metal salts (e.g., Al(CH₂--CH)·(CH₃)₂ for the formation of an Ae thin film and NiCO₄ for theformation of an Ni thin film) are usable. When a thin film of an alloyis formed, a mixed gas of chlorides of the corresponding metalcomponents is used. For the formation of a thin film of galliumarsenide, a mixed gas of (CH₃)₃ +AsH₃ is used. Gases consisting of othercomponents, compounds or elements enable the film formation in the samemanner.

Since the thermions from the filament 7 effectively contribute to theionization of the vapor in the container 1, the ionization of thematerial vapor is possible even in a high vacuum of not more than 10⁻⁴Torr. It is therefore possible to provide a thin film having a verydense structure. Although it is generally said that the density of athin film is lower than that of the bulk, a thin film having a densityvery close to that of the bulk is provided according to the firstembodiment. Furthermore, according to the first embodiment, since filmformation in a high vacuum is possible, only a few gas molecules aretaken into the thin film formed, thereby forming a thin film of highpurity. Therefore, an apparatus for forming a thin film according to thefirst embodiment is very suitable for the formation of semiconductorthin films constituting LSI and IC, etc. and metal thin films of highpurity which are used as the electrodes thereof.

In short, an apparatus according to the first embodiment is a completelynew apparatus which can realize both the merit of CVD and the merit ofPVD, the former being that it is possible to provide a thin film withstrong reactivity and the latter being that film formation is executedin a high vacuum which enables the formation of a dense and strong thinfilm. Since the vapor is ionized and has electrically high energy (thetemperatures of electrons and ions), it is possible to realize the filmformation which require reactivity and crystallization without providingheat energy in the form of temperature (reaction temperature andcrystallization temperature), thereby enabling film formation at a lowtemperature. A plastic sheet or the like having a low heat resistancemay therefore be used as the substrate 16. In addition it is possible toform a thin film excellent in the physical properties such as electricalcharacteristics, optical characteristics, crystallizability, density andadhesion with the substrate.

If a high-frequency electrode which produces a high-frequencyelectromagnetic field is disposed between the grid 6 and the counterelectrode 5, the ionization of the vapor is further accelerated by thehigh-frequency electromagnetic field, thereby enhancing theabove-described various effects.

A second embodiment of the present invention will be explained in thefollowing with reference to FIG. 2. The same reference numerals areprovided for the elements that are the same as those in the firstembodiment, and explanation thereof will be omitted.

In the container 1, electrodes 9, 11, 111, 112 and 113, which also serveas supporters, are provided. The electrodes 9, 11, 111, 112 and 113extend to the outside of the container 1 through the base plate 2 in anairtight relationship with the interior of the container 1 while beingkept electrically insulated from the base plate 2. These electrodes 9,11, 111, 112 and 113 constitute the electrically conducting meanstogether with other wiring means, power sources, etc.

A counter electrode 105 is disposed at the end portion of the electrode9 in a fixed state.

The electrode 112 is provided with a first grid 106a and the electrode113 is provided with a second grid 106b.

The filament 7 is held by the pair of electrodes 11. A source ofevaporation 108 is provided on the pair of electrodes 111.

The source of evaporation 108 held by the pair of electrodes 111 is ameans for evaporating substances being evaporated and has a resistanceheating system composed of a metal such as tungsten and molybdenumformed into a coil. The metal may be formed into a shape of a boat inplace of a coil. Alternatively, it may be a source of evaporation usingelectron beams which are used in a conventional vacuum evaporationsystem.

The filament 7, the grid 106a and the grid 106b are disposed between thesource of evaporation 108 and the counter electrode 105 in the container1 in that order from the source of evaporation 108 toward the counterelectrode 105.

The first and second grids 106a and 106b have a configuration whichallows the substances being evaporated to pass therethrough. In thisembodiment, they are composed of a plurality of linear wire electrodesarranged in parallel to each other with an equal space therebetween.

An AC power source 120 for heating is connected to the pair ofelectrodes 111 which support the source of evaporation 108, and the pairof electrodes 11 which support the filament 7 are connected to a DCpower source 122.

The positive electrode of a DC power source 121 is connected to theelectrode 112 which supports the grid 106a, and the negative electrodethereof is connected to the electrode 9. Therefore, the grid 106a has apositive potential relative to the potential of the counter electrode105.

The electrode 113 which supports the grid 106b is connected to thepositive electrode of a DC power source 123, and the negative electrodeside thereof is connected to the electrode 9. Therefore, the grid 106balso has a positive potential relative to the potential of the counterelectrode 105. The voltages of the power sources 121 and 123 are set sothat the potential of the grid 106b is lower than that of the grid 106a.The electrode 113 which supports the grid 106b may be connected to thenegative electrode of the DC power source 123 or directly grounded notthrough the power source 123 so that the potential of the grid 106b islower than that of the grid 106a. The negative electrode of the powersource 122 may be grounded, and an AC power source may be used in placeof the power source 122. The grounding shown in FIG. 2 is notnecessarily required. Actually, various operating switches are providedas a part of electrical conducting means and by operating these switchesthe film forming process is executed, but these switches are omittedhere.

A thin film is formed in the following way.

A substrate 100 for deposition is held by the counter electrode 105 soas to oppose the source of evaporation 108, as shown in FIG. 2.

The substances being evaporated are held by the source of evaporation108. The substances being evaporated are selected in accordance with thetype of a thin film to be formed. They are, for example, a metal such asaluminum and gold, an oxide, fluoride and sulfide of a metal, and analloy.

A gas is introduced into the vacuum container 1 in the same way as inthe first embodiment.

If the apparatus is operated in this state, the substances beingevaporated which are held by the source of evaporation 108 evaporate.The evaporated substances fly dispersively toward the substrate 100through the grid 106a. The thermions which are emitted from the filament7 also fly toward the grid 106a while being accelerated by the effect ofthe electric field formed by the grids 106a and 106b. When the thermionshit on the particles of the flying evaporated substances and theintroduced gas particles in the vicinity of the grid 106a, the thermionsionize these flying evaporated substances and gas particles. Thus,plasma is realized in the space in the vicinity of the grid 106a.

The particles of the ionized evaporated substances are accelerated bythe effect of the electric field directed from the grid 106a to the grid106b and hit on the substrate 100 through the grid 106b. Thus, a desiredthin film is formed on the substrate 100.

A uniform plasma state is realized in the vicinity of the substrate 100by the effect of the grid 106b. The plasma state involves a periodicstructure which corresponds to the configuration of the grid, but sincethe grid 106b moves, the plasma state becomes quite uniform relative tothe substrate 100. The thin film formed therefore has uniform thicknessand uniform physical properties.

Since a thin film is formed by the collision of the ion particles, ithas good adhesion with the substrate 100, and good crystallizability andorientation property.

In the second embodiment, since the ionization ratio of the substancesbeing evaporated is very high and stable, it is possible to obtain athin film having desired physical properties reliably by using variousgases and substances being evaporated in the same way as in the firstembodiment.

Since the thermions from the filament 7 effectively contribute to theionization of the evaporated substances and the introduced gas, it ispossible to ionize the evaporated substances even in a high vacuum ofnot more than 10⁻² Pa, so that only a few gas particles are taken intothe formed thin film, thereby forming a thin film of high purity. It isalso possible to provide a thin film having a very dense structure.

Although the first and second grids are composed of a plurality oflinear electrodes arranged in parallel to each other with an equal spacetherebetween and only the second grid is moved in the second embodiment,the first grid may also be moved in the same way as the second grid.

FIG. 3 shows another example of the configuration of the first gridand/or the second grid.

The configuration of the grid is represented in the polar coordinates(r, θ), rmm and θrad by the sum of the region represented by

    r≧a·θ/π

    r≦b+a·θ/π

and the region represented by

    θ≧k·2π/n

    θ≦d+k·2π/n

wherein r₀ ≦r≦r₁, k=0, 1, . . . n -1 (n: natural number).

Such a grid may be rotated around the origin of the coordinates by usinga rotary motion of a rotating machine during the formation of a thinfilm.

A third embodiment of the present invention will be explained in thefollowing with reference to FIG. 4. The same reference numerals areprovided for the elements that are the same as those in the first andsecond embodiments, and explanation thereof will be omitted.

In the container 1 the counter electrode 105, a grid 206, the filament 7and the source of evaporation 108 are provided with an appropriate spacetherebetween in that order from the top to the bottom. These members105, 206, 7 and 108 are supported in a horizontal state by theelectrodes 9, 10, 11 and 111, respectively, which also serve as thesupporters. These electrodes 9, 10, 11 and 111 extend to the outside ofthe vacuum container 1 through the base plate 2 while being keptelectrically insulated from the base plate 2. These electrodes 9, 10, 11and 111 electrically connected and feed the members inside and outsideof the container 1 and can constitute the electrically conducting meanstogether with other wiring means. Airtightness is secured at theportions through which the electrodes 9, 10, 11 and 111 extend to theoutside of the container 1.

The grid 206 supported by the electrode 10 has a structure having spaceswhich allow the material vapor to pass therethrough. For example, thegrid 206 is reticulate.

The power source means 17 for establishing a predetermined potentialrelationship between the counter electrode 105, grid 206, filament 7 andsource of evaporation 108 is provided outside the container 1 andconnected to each member through the electrodes 9, 10, 11 and 111.

The source of evaporation 108 is connected to an AC power source 215 forheating through the electrode 111. A DC power source 216 is provided,and the positive electrode of the DC power source 216 is connected tothe grid 206 via the electrode 10 and its negative electrode isconnected to the counter electrode 105 via the electrode 9. The grid 206has a positive potential relative to the potential of the counterelectrode 105. Therefore, the electric field between the grid 206 andthe counter electrode 105 is directed from the grid 206 to the counterelectrode 105. The filament 7 is connected to both ends of a DC powersource 217 via the pair of electrodes 11. Although the positive side ofthe DC power source 217 is grounded in FIG. 4, the negative side may begrounded. In place of the DC power source 217, an AC power source may beused. These power sources 215, 216 and 217 constitute the power sourcemeans 17, but the grounding shown in FIG. 4 is not necessarily required.

Actually, the power source means 17 includes various switches foreffecting electrical connections and by operating these switches a thinfilm is formed on the substrate 100, but these switches are omittedhere.

In this embodiment, the grid 206 is not provided in a fixed state, butit is connected to a driving mechanism 218 so as to be movable on apredetermined track. The driving mechanism 218 may be any of the knownrotation introducing machines, linear motion introducing machines or acombination thereof that allows the grid 206 to move on a track in thecontainer 1 by rotary motion, linear motion or a combination thereof. Inthis embodiment, the power of a motor 219 disposed outside the container1 is transmitted to the grid 206 through a rotation introducing device220, bevel gears 221, 222, 223 and 224 and a bearing 225, therebyrotating the grid 206 on a predetermined track. More specifically, thegrid 206 has the gear 224 which is supported in such a manner as to berotatable in a horizontal plane through the bearing 225 with respect tothe electrode 10 (in the electrically connected state) and whichinterlocks with the gear 223. The driving mechanism 218 is made of amaterial which can keep electrical insulation between the grid 206 andbell jar 3.

A thin film is formed by using the third embodiment described above inthe following way.

The substrate 100 is held by the counter electrode 105 and thesubstances being evaporated are held by the source of evaporation 108 inthe same way as in the second embodiment.

A gas is introduced into the vacuum container 1 in the same way as inthe first embodiment.

If the apparatus is operated in this state, the substances beingevaporated which are held by the source of evaporation 108 evaporate.The evaporated substances fly dispersively toward the substrate 100through the grid 206. Thermions are emitted from the filament 7 which isheated by the DC power source 217. The thermions emitted from thefilament 7 also fly toward the grid 206 while being accelerated by theaction of the electric field between the grid 206 and the counterelectrode 105. When the thermions hit on the particles of the flyingevaporated substances and the introduced gas in the space in thevicinity of the grid 206, the thermions ionize these particles. Thus,plasma is realized in the space in the vicinity of the grid 206.

The particles of the ionized evaporated substances are accelerated bythe effect of the electric field directed from the grid 206 to thecounter electrode 105 and hit on the substrate 100 at a high speed.Thus, a desired thin film is formed on the substrate 100. Since a thinfilm is formed of the ionized evaporated substances, it has goodadhesion with the substrate 100, and good crystallizability andorientation property.

During the formation of a thin film, the grid 206 is rotated on apredetermined track by the driving mechanism 218. It is thereforepossible to form a thin film having a uniform thickness over the entiresurface without producing the unevenness caused by the geometricalpattern of the grid 206. This is because the effect of shielding theevaporated substances by the geometrical pattern of the grid 206 ishorizontally averaged by the rotational movement or the like of the grid206.

As described above, in the third embodiment, since the ionization ratioof the substances being evaporated is very high and stable, it ispossible to obtain a thin film having desired physical propertiesreliably by using various gases and substances being evaporated in thesame way as in the first embodiment.

Since the thermions from the filament 7 effectively contribute to theionization of the evaporated substances and introduced gas, it ispossible to ionize the evaporated substances even in a high vacuum ofnot more than 10⁻² Pa, so that only a few gas particles are taken intothe formed thin film, thereby forming a thin film of high purity. It isalso possible to provide a thin film having a very dense structure. Thefilm thickness and the resistance of a thin film are made uniform. Thus,an apparatus for forming a thin film according to the third embodimentis very suitable for the formation of semiconductor thin filmsconstituting LSI and IC, etc., thin metal films of high purity used forelectrodes, and optical thin films.

In short, an apparatus according to the third embodiment is a completelynew apparatus which can realize both the merit of CVD and the merit ofPVD, the former being that it is possible to provide a thin film withstrong reactivity and the latter being that film formation is executedin a high vacuum which enables the formation of a dense and strong thinfilm. Since the evaporated substances are ionized and have electricallyhigh energy (the temperatures of electrons and ions), it is possible torealize the film formation which requires reactivity and crystallizationwithout providing heat energy in the form of temperature (reactiontemperature and crystallization temperature), thereby enabling filmformation at a low temperature. A plastic sheet or the like having a lowheat resistance may therefore be used as the substrate 100. In addition,since the grid 206 is rotated on a predetermined track in the vacuumcontainer during the formation of a thin film, the geometrical patterndrawn by the grid produces the effect of shading the substancesuniformly at each portion of the substrate, thereby greatly decreasingthe unevenness in the film thickness. Therefore, the third embodimentcan improve the productivity of IC, LSI, etc. and the quality of anoptical thin film so that it is applicable to the field ofsemiconductors and optical fields.

Various changes and modifications may be effected within the spirit andscope of the present invention as described herein above, not limited bythe embodiments.

What is claimed is:
 1. An apparatus for forming a thin film comprising:avacuum container evacuated to high vacuum and receiving a gas for vapordeposition therein, generation means for generating a vapor of amaterial for vapor deposition and introducing said vapor into saidcontainer, a counter electrode disposed within said container andholding a substrate to be vapor-deposited on a curved holding surfacethereof, said holding surface opposing said generation means with asubstantially equal distance from said generation means at all pointsthereof, an electrical potential of said electrode set equal or negativerelatively to an electrical potential of said generation means, a griddisposed between said generation means and said electrode for allowingsaid vapor to pass therethrough and accelerating said vapor, a surfaceof said grid being adapted to have an equal distance from said holdingsurface, an electrical potential of said grid set positive relatively tosaid potential of said generation means, said grid being adapted to havea curved grid surface which is parallel to said curved holding surface;and a filament disposed between said generation means and said grid foremitting thermions to ionize said vapor.
 2. An apparatus according toclaim 1, wherein said gas comprises an active gas, an inert gas or amixture of said active gas and said inert gas.
 3. An apparatus accordingto claim 1, wherein said generation means comprises a source ofevaporation of either a resistance heating type or an electron beam typefor evaporating a substance as said vapor within said container.
 4. Anapparatus according to claim 1, wherein said generation means comprisesan evaporation injector for injecting an evaporated substance asmaterial vapor within said container.
 5. An apparatus according to anyone of claims 1 to 4, wherein said curved holding surface and curvedgrid surface are concentric sphere surfaces.
 6. An apparatus for forminga thin film comprising:a vacuum container evacuated to high vacuum andreceiving a gas for vapor deposition therein, generation means forgenerating a vapor of a material for vapor deposition and introducingsaid vapor into said container, a counter electrode disposed within saidcontainer and holding a substrate to be vapor-deposited such that saidsubstrate opposes said generation means, a first grid disposed betweensaid generation means and said electrode for allowing said vapor to passtherethrough and accelerating said vapor, an electrical potential ofsaid first grid set positive relatively to an electrical potential ofsaid electrode, a second grid disposed between said first grid and saidelectrode in the vicinity of said electrode for allowing said vapor topass therethrough and accelerating said vapor, an electrical potentialof said second grid set negative relatively to said potential of saidfirst grid, and a filament disposed between said first grid and saidgeneration means for emitting thermions to ionize said vapor.
 7. Anapparatus according to claim 6, wherein said gas comprises an activegas, an inert gas or a mixture of said active gas and said inert gas. 8.An apparatus according to claim 6, wherein said generation meanscomprises a source of evaporation of either a resistance heating type oran electron beam type for evaporating a substance as said vapor withinsaid container.
 9. An apparatus according to claim 6, wherein saidgeneration means comprises an evaporation injector for injecting anevaporated substance as said vapor within said container.
 10. Anapparatus for forming a thin film comprising;a vacuum containerevacuated to high vacuum and receiving a gas for vapor depositiontherein, generation means for generating a vapor of a material for vapordeposition and introducing said vapor into said container, a counterelectrode disposed within said container and holding a substrate to bevapor-deposited such that said substrate opposes said generation means,a grid disposed between said generation means and said electrode forallowing said vapor to pass therethrough and accelerating said vapor, anelectrical potential of said grid set positive relatively to anelectrical potential of said electrode, a filament disposed between saidgrid and said generation means for emitting thermions to ionize saidvapor, and moving means for moving said grid with respect to saidelectrode on a predetermined track.
 11. An apparatus according to claim10, wherein said gas comprises an active gas, an inert gas or a mixtureof said active gas and said inert gas.
 12. An apparatus according toclaim 10, wherein said generation means comprises a source ofevaporation of either a resistance heating type or an electron beam typefor evaporating a substance as said vapor within said container.
 13. Anapparatus according to claim 10, wherein said generation means comprisesan evaporation injector for injecting an evaporated substance as saidvapor within said container.